linux-kernel - Re: [PATCH 3/4] sched/topology: move comment about asymmetric node setups

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Date:   Fri, 21 Apr 2017 18:31:26 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Lauro Ramos Venancio <lvenanci@...hat.com>
Cc:     lwang@...hat.com, riel@...hat.com, Mike Galbraith <efault@....de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] sched/topology: move comment about asymmetric node
 setups

On Thu, Apr 20, 2017 at 04:51:42PM -0300, Lauro Ramos Venancio wrote:
> @@ -612,7 +604,16 @@ static void init_overlap_sched_group(struct sched_domain *sd,
>  
>  		sibling = *per_cpu_ptr(sdd->sd, i);
>  
> -		/* See the comment near build_group_mask(). */
> +		/*
> +		 * Asymmetric node setups can result in situations where the
> +		 * domain tree is of unequal depth, make sure to skip domains
> +		 * that already cover the entire range.
> +		 *
> +		 * In that case build_sched_domains() will have terminated the
> +		 * iteration early and our sibling sd spans will be empty.
> +		 * Domains should always include the CPU they're built on, so
> +		 * check that.
> +		 */
>  		if (!cpumask_test_cpu(i, sched_domain_span(sibling)))
>  			continue;
>  

FWIW, the topology that spawned all that is:

  10,20,20,30
  20,10,20,20
  20,20,10,20
  30,20,20,10